The IAS machine was a binary computer with a 40-bit word, storing two 20-bit instructions in each word. The memory was 1024 words (5.1 kilobytes). Negative numbers were represented in "two's complement" format. It had two general-purpose registers available: the Accumulator (AC) and Multiplier/Quotient (MQ). It used 1700 vacuum tubes (triode types: 6J6, 5670, 5687, a few diodes: type 6AL5, 150 pentodes to drive the memory CRTs, and the 40 memory CRTs).[9] The memory was originally designed for about 2300 RCASelectronvacuum tubes. Problems with the development of these complex tubes forced the switch to Williams tubes.

It was an asynchronous machine, meaning that there was no central clock regulating the timing of the instructions. One instruction started executing when the previous one finished. The addition time was 62 microseconds and the multiplication time was 713 microseconds.

Although some claim the IAS machine was the first design to mix programs and data in a single memory, that had been implemented four years earlier by the 1948 Manchester Baby.[11] Also MESM became operational prior to the IAS machine.

Von Neumann showed how the combination of instructions and data in one memory could be used to implement loops, by modifying branch instructions when a loop was completed, for example. The resultant demand that instructions and data be placed on the same memory later came to be known as the Von Neumann bottleneck.

Plans for the IAS machine were widely distributed to any schools, businesses, or companies interested in computing machines, resulting in the construction of several derivative computers referred to as "IAS machines," although they were not software compatible in the modern sense.[4]